[exim] Modify headers based on MySQL lookup

Hi there,

I want to modify the message headers (prepend some text to the subject)
based on whether or not the $sender_address is in a database. I've tried
a system filter, but it appears to lack the capability to do a mysql
lookup. I've tried a router, but it lacks the ability to add/remove
headers.

What is the best method to accomplish this?


cheers
Michael